Cylindrical holograms viewable in monochromatic light are described by Dr. Tung Jeong. Dr. Jeong describes a single-step process wherein an object is placed inside a cylinder of holographic film and both object and film are illuminated simultaneously by a laser beam diverging from a point on the axis of the cylinder. Light scattering from the object interferes with the light directly illuminating the film and produces an interference pattern on the film. The exposed film is developed to yield a hologram of the object, viewable by rolling the film into a cylinder and illuminating it with monochromatic light from a point on the axis corresponding to the point from which the reference beam diverged. The important disadvantage of Dr. Jeong's process is that the hologram requires an expensive monochromatic illuminating source, such as filtered mercury arc lamp or a laser.
Another prior art cylindrical hologram is the "Cross" hologram, such as is described in U.S. Pat. No. 4,206,956. The Cross hologram is synthesized from a large number of two-dimensional images and is analogous to a lenticular photograph. While the Cross hologram is viewable in white light, it must be manufactured by a complex process requiring precision equipment, and it requires production of a motion picture film under special conditions.
Also in the prior art is a hologram covered by U.S. Pat. No. 3,633,989, by Dr. Steven Benton. Dr. Benton's patent primarily covers a means of producing an information-limited hologram of a subject for the purpose of making a white-light viewable image. The method white-light viewable holograms, but will not work for making cylindrical holograms, without cumbersome optical systems for forming and reconstructing holograms in a cylindrical symmetrical arrangement. The method calls for forming a real image of the subject of the hologram and limiting the vertical parallax of the light forming the real image.
Several workers in the field have attempted to copy cylindrical holograms by flattening an original cylindrical hologram, then reconstructing to form a second hologram on a plane parallel to the plane of the flattened original, but at a distance away. An example of such attempts is described in U.S. Pat. No. 4,339,168. One purpose of the attempts was to create a second hologram which formed a cylinder of smaller diameter, but which contained an image of the original size; another purpose was to create a second hologram whose image intersected the plane of the film.
These attempts did not simply work poorly. They failed utterly because flattening the cylinder rearranges the wavefront in such a way that the image is severely distorted and has no well-defined location. Haines' two-step method is inherently incapable of compensating for the distortions caused by changing the shapes of the holograms.
Prior to the present invention, there was no known method for creating a white-light viewable hologram other than multiplexed holograms of cylindrical "Cross" type, described in U.S. Pat. No. 4,206,956 by Stephen P. McGrew.
Prior art relating to spatial filtration of wavefronts is well represented by the teaching of Dr. Steve Benton (U.S. Pat. No. 3,633,989). Benton describes a method for producing white-light viewable holograms wherein a first hologram is constructed at a certain location (which we will call the "viewing location"); then a second hologram is formed at the real image position from the real image reconstructed when a long horizontal strip of the first hologram is illuminated by the conjugate to its reference beam.
In Benton's method, restricting the reconstructed portion of the first hologram to a horizontal strip is a form of spatial filtering. Once the first hologram has been made, there is no choice of viewing location.
The cylindrical Cross hologram and T. Jeong's cylindrical laser-viewable hologram are prior art cylindrical holograms. The Cross hologram is made in a series of steps including production of a cinema film. Jeong's hologram is made in a single step and is not white-light viewable.